Global proteomic analysis of water buffalo (Bubalus bubalis) saliva at different stages of estrous cycle using high throughput mass spectrometry.

Accurate and efficient detection of estrus is one of the major constraints for exploitation of the production potential of buffalo owing to its poor manifestation of estrus signs, seasonal differences in expression and higher incidences of silent estrus (29%). The current study focused on identification of estrus specific candidate proteins in saliva of buffaloes. Estrus was detected based on behavioral signs in response to the teaser and changes in reproductive organs and confirmed by per-rectal examination, trans-rectal USG of reproductive organs, cervico-vaginal mucus characteristics and blood serum progesterone estimation. Day of onset of estrus was considered as day 0 and day -3, +3, +10 were considered as proestrus, metestrus and diestrus stage of the estrous cycle respectively. A total of 19 animals and their 38 estrous cycles (two from each) were included in this study. Saliva was collected from these animals during different stages of estrous cycle. Out of these, 08 animals were selected for global proteome analysis of saliva using in-solution digestion and nano-LC-MS/MS. A total of 275, 371, 304 and 565 proteins were identified with ≥2 peptides during proestrus, estrus, metestrus and diestrus stages of estrous cycle. Among the identified proteins 31, 62, 32 and 104 proteins were found specific to proestrus, estrus, metestrus and diestrus stage of the estrous cycle. Few salivary proteins such as Cullin-associated NEDD8-dissociated protein 1, Heat shock 70 kDa protein 1A, 17-beta-hydroxysteroid dehydrogenase type 1, Inhibin beta A chain, testin were identified as estrus specific and are important for estrus physiology. Taken together, these estrus specific proteins could be considered as the candidate biomarker for detection and confirmation of estrus in buffalo after thorough validation.